1. Field of the Invention
The present invention relates generally to a windshield wiper system for an automotive vehicle, and more particularly to a windshield wiper system for an automotive vehicle in which the intermittent time intervals of the wiper operations can be controlled in accordance with the time elapsed and the distance travelled, so that an adequate intermittent wiper operation can usually be achieved in inclement weather such as drizzle or light rain, especially when the vehicle is travelling at a low speed or has stopped.
2. Description of the Prior Art
The windshield wiper apparatus for an automotive vehicle is so designed as to be operable at high speed or at low speed by selectively depressing the switches thereof. However, in some wiper systems an intermittent wiper operation system is additionally provided therewith, which is usually especially effective in such bad weather as drizzle or light rain when continuous wiper operation may annoy the driver.
The intermittent time intervals of the wiper operation are generally determined by an intermittent time signal obtained by dividing a constant reference frequency generated from an oscillator. However, since it is desirable to adjust the time intervals manually or automatically according to the amount of rain striking the windshield, there exist windshield wiper systems in which the time intervals of the intermittent wiper operation can be adjusted. In the conventional intermittent-operation windshield wiper systems described above, the time intervals of the intermittent wiper operation are controlled from the standpoint that the amount of rain striking the windshield increases in proportion to the speed of the vehicle. However, the amount of rain is not closely related to a function of vehicle speed. This is because the amount of rain on the windshield is controlled by two factors based on the horizontal projection of windshield area and the vertical projection of that area. That is to say, one factor of the amount of rain on the windshield is based on the horizontal projection of windshield area, and has a close relationship to the time elapsed during the rainfall. Another factor of the amount of rain on the windshield is based on the vertical projection of windshield area, and has a close relationship to the distance travelled. This may easily be understandable from the fact that rain strikes the windshield even when the vehicle is parked. Therefore, it is not practical to control the period of the windshield wiper's intermittent operation on the basis of a function of vehicle speed only, since the amount of rain on the windshield is significant even when the vehicle speed is zero. In addition to the above problem, it is necessary to calculate a mean vehicle speed because it is practically impossible to control the time intervals of the wiper operation on the assumption that the instantaneous amount of rain is proportional to the instantaneous vehicle speed. Thus, an integration circuit is additionally required, thereby raising the problem that the system may be complicated and would therefore be costly.
A more detailed description of an example of the prior-art windshield wiper system will be made hereinafter with reference to FIG. 1.